Multimedia and group communications are becoming more important aspects of telecommunication networks, and the demand for such services will continue to increase. For instance, there are presently many different systems and networks that allow group communication. Public safety organizations are particularly interested in group communications and dedicated resources are being provided for these organizations. Businesses and even personal users also have a desire to use multimedia and group communication. As a result a suite of protocols have already been developed for use in multimedia communications. These protocols are used to control broadcast and interactive communications sessions including data streams such as audio (voice), video, text messaging, and internet protocols, for example between, or to, users (also referred to herein as subscribers) in a communications network. Each subscriber is typically associated with a communications device (also referred to herein as a subscriber unit) that is connected to the communications network.
In practice, a subscriber or dispatcher can set up a multimedia group call with a defined set of users or can allow users to join an existing group call. The multimedia group call consists of establishing a session with different application streams or flows that each represent a different media type, such as voice or video for example. A subscriber attempting, or paged, to join the group call is required to go through session and resource negotiations with a server supporting that session before being able to join the session. This session and resource negotiation requires considerable messaging overhead in the network, which can cause bandwidth and timing problems that are not desirable for sensitive communications, such as in the area of public safety.
In addition, it may be that during the negotiation it is found that the subscriber unit does not have the capability or resources to handle one or more of the different application streams or flows for that group session, whereupon the session can not be completed, wasting all of the previous negotiation messaging. For example, this may occur if the subscriber unit does not have video capability. This may also occur if the subscriber unit is in another session that loads some of its resources, and therefore it is not able to fully participate in the full new group session. This may also occur if the subscriber unit has priority or cost restrictions, and therefore it is not able to fully participate in the full new group session.
Known systems for group communication have implemented a server-centric call control architecture. This architecture may be included in a push-to-talk (PTT) communications system, for example. The architecture includes a service-specific group server, which may be for instance a PTT server, that can be communicatively coupled in the signaling path with a plurality of subscriber units, and optionally a dispatcher, as is known in the art.
The group communication is a session supported by the group server, which is known to subscriber units as the target for all call control signaling. To setup a session, an initiating subscriber unit or dispatcher establishes the group call and its required applications (e.g. voice and video) on the group server. Call control signaling identifies the subscriber units in the group in some manner. These subscriber units are then contacted in a group page by the server, which negotiates with each subscriber unit using a signaling transaction in a separate call leg to join that unit to the session. In addition, other subscriber units can join an established session later through the same negotiation procedure. However, as the number of group members increases, more and more signaling exchanges must be performed over the available communication links before session connection can be completed, if that is even possible for some units with limited resources. For large groups, serialization delays can increase call setup times beyond what is acceptable for certain systems, especially public safety dispatch systems.
Therefore, a need exists for a method and call control architecture that uses less messaging overhead to establish or join a multimedia group session. It would also be of further benefit to identify earlier those subscriber units that do not have sufficient resources for part or all of the group communication session.